Radio Communication System, Radio Communication Method and Base Station

1. A radio communication system including: a serving cell configured to transmit, to a radio terminal, an absolute grant for directly specifying an uplink user data transmission rate and a relative grant for relatively specifying the uplink user data transmission rate: and a non-serving cell configured to transmit the relative grant to the radio terminal without transmitting the absolute grant, wherein the non-serving cell includes an instruction unit configured to instruct the serving cell to decrease the uplink user data transmission rate, when a reception power of uplink user data exceeds a predetermined interference threshold.

2. The radio communication system according to claim 1 , wherein the non-serving cell includes a first selection unit configured to select, from a plurality of radio terminals, a radio terminal whose uplink user data transmission rate is to be decreased, when the reception power of the uplink user data exceeds the predetermined interference threshold, and the instruction unit notifies, to the serving cell, the radio terminal selected by the first selection unit.

3. The radio communication system according to claim 1 , wherein the non-serving cell includes a first determination unit configured to determine a decrease amount of the uplink user data transmission rate, when the reception power of the uplink user data exceeds the predetermined interference threshold, and the instruction unit notifies, to the serving cell, the decrease amount determined by the first determination unit.

4. The radio communication system according to claim 1 , wherein the serving cell includes a second selection unit configured to select, from a plurality of radio terminals, a radio terminal whose uplink user data transmission rate is to be decreased, when the non-serving cell instructs the serving cell to decrease the uplink user data transmission rate.

5. The radio communication system according to claim 1 , wherein the serving cell includes a second determination unit configured to determine a decrease amount of the uplink user data transmission rate, when the non-serving cell instructs the serving cell to decrease the uplink user data transmission rate.

6. The radio communication system according to claim 4 , wherein the second selection unit selects a radio terminal having an uplink user data transmission rate larger than a predetermined transmission rate.

7. The radio communication system according to claim 4 , wherein the second selection unit selects a radio terminal performing a handover from the serving cell to the non-serving cell.

8. The radio communication system according to claim 5 , wherein the decrease amount is determined not to decrease the uplink user data transmission rate to below a predetermined transmission rate.

9. A radio communication method including a serving cell configured to transmit, to a radio terminal, an absolute grant for directly specifying an uplink user data transmission rate and a relative grant for relatively specifying the uplink user data transmission rate; and a non-serving cell configured to transmit the relative grant to the radio terminal without transmitting the absolute grant, comprising: instructing, from the non-serving cell to the serving cell, to decrease the uplink user data transmission rate, when a reception power of uplink user data exceeds a predetermined interference threshold.

10. A base station provided in a radio communication system including: a serving cell configured to transmit, to a radio terminal, an absolute grant for directly specifying an uplink user data transmission rate and a relative grant for relatively specifying the uplink user data transmission rate; and a non-serving cell configured to transmit the relative grant to the radio terminal without transmitting the absolute grant, wherein the base station includes the non-serving cell including an instruction unit configured to instruct the serving cell to decrease the uplink user data transmission rate when a reception power of uplink user data exceeds a predetermined interference threshold.